Facial expressions are complex signals caused by rapid changes in facial muscular activity that are brief and last only a few seconds. Humans typically decode these signals during dynamic interactions in which the face moves. The present proposal aims to fulfill a gap in the literature regarding a well documented, but poorly explained phenomenon. Over the years, numerous studies have shown that the left side of the face is more emotionally expressive than the right. This asymmetry is more predominant for right- than left-handers and seems to occur for both negative and positive expressions. Even nonhuman primates such as the rhesus monkey have been reported to display more intense expressions over the left side of the face. The basis for these asymmetries is unclear. The most popular neuropsychological interpretation has been that this left hemi-face asymmetry is a consequence of a right hemisphere advantage in processing emotional material. Unfortunately, little progress has been made since the late 1970?s to more clearly articulate this position or to evaluate alternative explanations for observations that the left hemi-face is more intensely expressive than the right. The overall purpose of the proposed research is to examine three hypotheses that might contribute to our understanding of hemi-facial movement asymmetries and assess their viability using contemporary state-of-the-art methodologies. The specific aims of this project are: (a) to use trans-cranial magnetic stimulation (TMS) to learn whether the left lower hemi-face receives more cortical influence (either contra-lateral or ipsilateral) and determine whether this relates to behavioral asymmetries in dynamic facial expression; (b) to test the hypothesis of material specific (linguistic, emotion) hemispheric priming of contra-lateral motor systems; and (c) to test the hypothesis of lateralized inhibition of contra-lateral motor systems. A series of 6 studies are planned using cognitive priming, trans-cranial magnetic stimulation, and computer-based systems for digitizing dynamic facial signals. Either singly, or in combination, an increased understanding of these hypothesized mechanisms will likely contribute to our knowledge of expressive asymmetries and provide information that will ultimately be useful for examining emotional communication disturbances associated with psychiatric and neurologic disease in humans.